There have been proposed a number of electrophotographic photosensitive members having a photoconductive layer composed of an inorganic material such as amorphous selenium (A-Se), CdS, ZnO and amorphous silicon (A-Si) or an organic material.
However, for any of the known electrophotographic photosensitive members, there are still unresolved problems.
For instance, as for the known electrophotographic photosensitive member having a A-Se photoconductive layer, there is a limit for its use because its spectral sensitivity inclines toward the short wavelength side of visible region. In order to solve this problem, there is a proposal of incorporating Te or As into said A-Se photoconductive layer. For those electrophotographic photosensitive members having such A-Se series photoconductive layer containing Te or As, there can be recognized an improvement in the foregoing problem relating to the spectral sensitivity. However, they are still accompanied with various problems such as increase of a light fatigue, reduction of a charge-retentivity under a high temperature atmospheric condition, increase of a residual potential under a low temperature atmospheric condition, etc. which result in deterioration of the quality of the resulting image and also lack of the stability upon repeated use. Other than these, they have been accompanied by other problems in that the hardness of any of the foregoing photoconductive layers is relatively low, and because of this, especially in the case where the surface of said layer is not protected, when it is engaged repeatedly in the cleaning process in a high speed electrophotographic copying machine having an improved blade cleaning system, its surface becomes easily worn away producing fine particles which eventually intermix in developers, disperse in the copying machine, or otherwise, intermix in the resulting image.
Further in addition, for the foregoing electrophotographic photosensitive member, there is a further problem that because of a low crystallization temperature for selenium (Se), it will be easily crystallized with an incidental heat or with a light energy caused by light irradiation, and in that case, the charge-retentivity becomes reduced accordingly.
There are unresolved problems also for the known electrophotographic photosensitive members having a photoconductive layer composed of ZnO or CdS.
That is, in case of the electrophotographic photosensitive member having a photoconductive layer composed of ZnO, it is necessary to add an appropriate organic pigment in order for said layer to have a sufficient sensitivity against visible light. In addition to this, it is accompanied by a problem in that the photosensitivity is gradually decreased as it is used repeatedly and because of this, it is not suited for repeated use for a long period of time.
And, in case of the electrophotographic photosensitivity member having a photoconductive layer composed of CdS, there is a serious problem since CdS is harmful for a man. Therefore, not only extra attention but also provision of a specific means are necessary to be made in order to prevent occurrence of any environmental problems because of CdS not only in its production but also upon its use.
Now, for the known electrophotographic photosensitive members having a binder series photoconductive layer, there are also unresolved problems. That is, because of the specific requirement that photoconductive particles must be evenly dispersed in a resin binder, there exist a number of parameters to determine electric characteristics, photoconductive characteristics, and physical and chemical characteristics for a photoconductive layer to be prepared. And unless the related parameters are strictly coordinated, an objective desired photoconductive layer is hardly obtained. In addition, because of the uniqueness that the binder series photoconductive layer is a dispersion system and because of this, the layer is entirely of a porous structure, it is very sensitive against changes in the environmental humidity. And in the case where the electrophotographic photosensitive member having such photoconductive layer is used under highly humid environmental atmosphere, there will be easily produced a deterioration in the electric characteristics to thereby make it impossible to obtain a high quality image.
Also in case of other kinds of the known electrophotographic photosensitive members having a photoconductive layer composed of an organic photoconductive material, there still exist various unresolved problems in that the characteristics will be deteriorated during repeated use because of low corona discharging resistance, the cleaning properties are problematic for the reason that an organic polymer as well as toner is used, the surface is easily damaged because of weak mechanical strength and it is difficult to maintain the quality of an image obtained upon repeating use for a long period of time.
Further, for any known electrophotographic photosensitive member as mentioned above, there is another problem caused by occurrence of a friction between a cleaning blade and the photosensitive member which often invites undesirable effects not only in the cleaning properties but also in the electrophotographic properties, especially in case of using it in a high speed electrophotographic copying machine. For instance, it will become difficult to add a sufficient quantity of pressure between the cleaning blade and the photosensitive member in the case where the related coefficient of kinetic friction is large as much as to likely bring about undesirable influences especially on the electrophotographic characteristics.